Vibrato system for amplifiers



-TO VIBRATO April 1949. N. 1. DANIEL. 2,466,306

VIBRATO SYSTEM FOR AMPLIFIERS Filed Oct. 29, 1947 FIG-l.

IO TO VIBRATO I FREQ.- 05C.

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Patented Apr. 5, 1949 UNITED STATES PATENT OFFICE VIBRATO SYSTEM FORAMPLIFIERS Nathan I. Daniel, Long Branch, N. J.

Application October 29, 1947, Serial No. 782,838

3 Claims. 1

This invention relates to audio frequency amplifier devices and moreparticularly to an amplifier for a musical instrument or the likewherein the output is automatically provided with a tremolo or vibratoeffect.

This application is a continuation in part of my previous applicationfiled August 29, 1947, and bearing Serial No. 771,259.

As was disclosed in said prior application, it is well recognized that avibrato improves the quality of music and it is employed by accomplishedmusicians through supplementary manipulation of the strings or othersound producing elements of an instrument. However, not only must themusician be accomplished at his task, but it requires particular effortand attention while the human element involved often causes notes orpassages to be deprived of vibrato or to be insufficiently providedtherewith.

According to my prior application, I automatically produced a vibratoeffect in the output of the amplifier by employing a low frequencyoscillator which was connected to the control grids of the amplifieroutput tubes. The amplitude of the output was varied according to thelow frequency oscillator signals and the music issuin from the speakerof the amplifier was thereby provided with a vibrato or tremolo effect.However, if it were desirable or necessary to achieve a high intensityof vibrato, correspondingly high oscillator signals would have to be fedto the control grids of the output tubes. It is evident that under suchconditions the music could be distorted if the tubes were required tooperate along a non-linear portion of their characteristic curves. Inother words, an oscillator signal of high intensity might bring theplate current of a tube into a flattened portion of its curve so as toproduce distortion as is well understood in the art.

Bearing the foregoing in mind, it is an object of this invention toprovide an amplifier for musical instruments or any similar soundproducing medium wherein the sound output may be automatically providedwith a vibrato of practically unlimited intensity. The vibrato in factmay periodically cut off the output completely so that substantially100% vibrato may be secured. This object also includes the achievementof such vibrato without having any effect on the fidelity of theamplifier output, the foregoing being accomplished by avoiding action onthe tubes of the amplifier in modulating the output as required.

Another object of this invention is to provide a vibrato arrangementwhich is largely disassociated from an amplifier with which it isconnecte'd thereby enabling the arrangement to be separately producedand simply incorporated into an amplifier. Thus, a separate power supplyfor the vibrato system is produced, such an arrangement ofiering furtheradvantages as well.

Other objects of my invention will be apparent from the followingdescription, it being understood that the above general statements ofthe objects of my invention are intended to describe and not limit it inany manner.

Referring to the drawings:

Fig. 1 is a schematic view of the improved vibrato system such as may beincorporated into an audio amplifier.

Fig. 2 is a modified embodiment thereof.

As disclosed in my previous application, the amplifier itself may beconventional including a loud speaker having an exciting field winding.The present invention provides an apparatus for connection to suchspeaker field so that in effect the speaker efiiciency may be caused tovary at the sub-audio frequency rate of the vibrato oscillator. Thevibrato frequency oscillator or generator may take any conventional formof audio oscillator such as may be found in any radio handbook and inthe instant application I employ the term vibrato frequency oscillatorto indicate an oscillator operating approximately over a 3 to 20 cyclefrequency range. In my prior application I disclosed an oscillator ofthe resistance-capacity type which provides good stability and can beeasily controlled as to frequency. That oscillator or any other type maybe employed in the instant invention. The output of the oscillator isapplied to points Ill and H which are connected through condenser I! toa potentiometer l3 constituting the vibrato amplitude control. Condenserl2 may be .5 microfarad so as to present very little impedance to lowaudio frequencies while potentiometer l3 may be in the order of a halfmegohm. The arm M of potentiometer I3 is connected to the control grid15 of an electron discharge tube l6. Tube I6 is preferably, but notnecessarily, of the so-called power type tubes such as type 45 or type6L6. The purpose of preferring power tubes is that more current can behandled so as to adequately energize a speaker field. In fact, two ormore such tubes in parallel may be employed as by directly connectingthe plates, grids and cathodes together when the total field currentrequirements cannot be provided by a single tube. For example, one largespeaker field may require high currents or more than one speaker may beused in a system. The plate is of tube It is connected to the winding I9of the speaker field 2G. The other end of the speaker field winding isconnected to a suitable source of B+ voltage such as may be suppliedthrough the power supply of the amplifier. In other words, the speakerfield and tube 16 will be connected across the power supply of theamplifier.

As the grid I is fed the output of the oscillator which generates therequired fluctuating voltages of vibrato frequency, the plate current ofthe tube will vary correspondingly in an amplified manner. This varyingplate current flows through the speaker field and varies its excitationfunction accordingly so that the varying vibrato currents are fed, fromthe output of the tube, to the voice coil of the speaker, by theconventional electro-magnetic action of such speakers. The speakerefiiciency is thus caused to vary in the vibrato frequency and the musicproduced by the amplifier and speaker is thereby modulated by thevibrato currents. Such music is fed from the audio signal channel 2|which is the source of audio frequency signals, to the voice coil 22,the speaker cone 23 being actuated accordingly. It will be noted thatthe vibrato action is independent of the amplifier or audio signalchannel so as to avoid any tendency to distortion of the audio signals.

The second embodiment employs a separate power supply from that of theamplifier and discloses a full wave rectifier arrangement whichincorporates the speaker field as a load. Transformer type 25 may be ofthe usual step-up type and the respective ends of its secondary windingare connected to plate 26 of tube 2'! and plate '28 of tube 29. Tubes 21and 29 may be of the power type as above described. The cathodes of thetubes are connected together as are the control grids 30 and 3|. Thespeaker field winding 32 is connected from the mid-point 33 of the powertransformer secondary to cathode midpoint 34 which may be a high voltagepoint relative to point 33. Potentiometer 35 and condenser 36 servesubstantially the same function as potentiometer I3 and condenser [2 inthe previous embodiment. Resistor 38 is a grid return of conventionalhigh resistance. Condenser 31 is a filter condenser which may have avalue of 8 mfd.

The operation of the circuit shown in Fig. 2 is essentially similar tothat of the previous embodiment. Briefly, the vibrato voltages are fedto the input circuit or control grids of the tubes 21 and 29 Whichoperate as grid control rectifiers and produce a varying and amplifiedvoltage across the speaker field 32. Corresponding currents will flowthrough the speaker field in the cathode or output circuit so as to varythe emciency of the speaker field in the manner above stated. Either thefull wave rectifier arrangement shown or a half wave rectifier may beemployed as will be self-evident to one skilled in the art. Thus, thesupply voltage, with or without a transformer, may be rectified acrosstheplate and cathode electrodes of a tube while the control grid isconnected to the vibrato oscillator, the

speaker field being in the plate circuit the audio signal channel, voicecoil, and speaker cone follow the arrangement shown in Fig. 1.

In the second embodiment, it is recognized that the filter condenser 31used to smooth out supply frequency ripples in the power supply, willtend to similarly smooth out the vibrato signals. However, the vibratosignals are generally of a frequency of about 3 to 20 times per secondwhile the filter condenser is generally chosen to be effective oncurrents of 60 cycle frequency. Therefore, if the filter condenser isapproximately 8 mid, it will be satisfactory for filtering theconventional 60 cycle frequency of the power supply output but will betoo small to smooth out the very low oscillator frequency. In thisarrangement, since a separate power supply is employed, the vibratosystem is almost fully independent of the amplifier and can be producedas a separate unit wherein it is only necessary to connect the speakerfield in the manner shown in order to provide the amplifier with thedesired vibrato.

It will be observed that in both of the above embodiments the amplifieroutput tubes are not affected since the vibrato is accomplished in thespeaker alone substantially independently of normal operation of theamplifier itself.

While there has been shown what at present is considered a preferredembodiment of the invention, it will be evident that many changes andmodifications may be made therein without departing from its spirit. Itis therefore aimed in the appended claims to cover all such changes andmodifications which fall within the true spirit and an audio signalchannel connected to said voice coil, vibrato means for said amplifier,said vibrato means comprising an electronic vibrato frequencyoscillator, at least one electron discharge tube having a control gridand an output circuit, said oscillator being connected to said controlgrid and the output circuit of said tube being directly connected tosaid field winding whereby the output of said tube flows through saidfield winding, the connection of said oscillator to said control gridbeing independent of said audio signal channel, said oscillator beingvariable in both amplitude and frequency, the frequency variation beingover a range of approximately 3 to 20 cycles per second.

2. In an audio amplifier including an audio signal channel, and aspeaker having electromagnetic means including an electromagneticallyactuated voice coil for driving the speaker cone, vibrato means for saidamplifier, said vibrato means comprising an electronic vibrato frequencyoscillator, electron discharge tube means having input and outputcircuits, said oscillator being connected to said input circuit, and theoutput circuit being electrically connected to said speakerelectromagnetic means whereby the currents fiowing in said outputcircuit are fed to said voice coil through electromagnetic action, theconnection of said oscillator to said input circuit being independent ofsaid audio signal channel, said oscillator being variable in bothamplitude and 5 6 frequency, the frequency variation being over a nel,the operating frequency of said oscillator berange of approximately 3 to20 cycles per second. ing less than approximately 20 cycles per second.3. In an audio amplifier including a speaker, NATHAN I. DANIEL. anexciting field winding therefor, a voice coil, and an audio signalchannel connected to said 5 REFERENCES CITED voice coil, vibrato meansfor said amplifier, said The following references are of record in thevibrato means comprising an electronic vibrato me of this patent:frequency oscillator, said oscillator being connected to said fieldwinding so as to feed its vi- UNITED STATES PATENTS brato frequencyoutput currents therethrough, 10 Number Name Date the connection of theoscillator to the fiel-d wind- 1,967125 Miner July 17 1934 ing beinindependent of said audio signal chan- 2,169,762 Kaye Aug. 15, 1939

